Parathyroid Hormone (PTH) – Function, Levels & Disorders
Parathyroid hormone (PTH) is a vital hormone produced by the parathyroid glands that regulates calcium and phosphate levels in the body, playing a key role for bones, kidneys, and the intestine.
Things worth knowing about "Parathyroid hormone"
Parathyroid hormone (PTH) is a vital hormone produced by the parathyroid glands that regulates calcium and phosphate levels in the body, playing a key role for bones, kidneys, and the intestine.
What is Parathyroid Hormone?
Parathyroid hormone (abbreviated PTH, also called parathormone) is a peptide hormone produced and secreted by the four small parathyroid glands located near the thyroid gland in the neck. PTH is the primary hormone responsible for regulating calcium levels in the blood and works closely together with vitamin D and the hormone calcitonin.
Mechanism of Action
PTH is released whenever blood calcium levels drop below normal. It acts on three main target organs:
- Bones: PTH activates bone-resorbing cells (osteoclasts), causing calcium and phosphate to be released from bone tissue into the bloodstream.
- Kidneys: PTH increases the reabsorption of calcium in the kidney tubules, promotes the excretion of phosphate, and stimulates the production of active vitamin D (calcitriol).
- Intestine: Through the activation of vitamin D, PTH indirectly enhances calcium absorption from food in the small intestine.
The overall goal of these mechanisms is to normalize and maintain blood calcium levels within a healthy range.
Normal Values and Measurement
PTH levels are measured through a simple blood test. Normal values in adults typically range between 15 and 65 pg/mL (picograms per milliliter), though reference ranges may vary slightly between laboratories. PTH is commonly measured alongside blood calcium, phosphate, and vitamin D levels to help diagnose parathyroid disorders.
Conditions Related to Parathyroid Hormone
Hyperparathyroidism (excess PTH)
In hyperparathyroidism, too much PTH is produced, leading to elevated blood calcium levels (hypercalcemia), bone loss, kidney stones, fatigue, muscle weakness, and gastrointestinal complaints. Three forms are distinguished:
- Primary hyperparathyroidism: Most commonly caused by a benign adenoma of one of the parathyroid glands.
- Secondary hyperparathyroidism: A compensatory response to chronic low calcium levels, for example in chronic kidney disease or vitamin D deficiency.
- Tertiary hyperparathyroidism: Autonomous PTH production following long-standing secondary hyperparathyroidism.
Hypoparathyroidism (insufficient PTH)
In hypoparathyroidism, too little PTH is produced, resulting in low blood calcium levels (hypocalcemia). Typical symptoms include tingling, muscle cramps (tetany), nausea, and in severe cases cardiac arrhythmias. The most common cause is accidental damage to or removal of the parathyroid glands during thyroid surgery.
Diagnosis
Diagnosis of PTH-related disorders is based on:
- Blood tests: PTH level, calcium, phosphate, vitamin D, and creatinine
- Urine tests: calcium excretion in a 24-hour urine collection
- Imaging: ultrasound, scintigraphy, or MRI of the parathyroid glands
- Bone density measurement (DXA scan) if bone involvement is suspected
Treatment
Treatment depends on the underlying condition:
- Hyperparathyroidism: Primary hyperparathyroidism is often treated surgically by removing the affected parathyroid tissue (parathyroidectomy). Secondary hyperparathyroidism is managed by treating the underlying cause and supplementing with vitamin D and calcium.
- Hypoparathyroidism: Treatment involves calcium and active vitamin D (calcitriol) supplementation. In selected cases, replacement therapy with recombinant PTH may also be considered.
References
- Bilezikian JP, Khan AA, Potts JT Jr. - Guidelines for the Management of Asymptomatic Primary Hyperparathyroidism. Journal of Clinical Endocrinology & Metabolism, 2014.
- Shoback D. - Hypoparathyroidism. New England Journal of Medicine, 2008; 359:391-403.
- World Health Organization (WHO) - Calcium and vitamin D supplementation guidelines. URL: https://www.who.int
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